The present invention relates to an austenitic stainless steel based on chromium, nickel and molybdenum.
More specifically it relates to austenitic stainless steel compositions usable in nuclear reactors, such as fast neutron reactors, particularly as the core structural material or as a material for canning fuel elements, which has a better resistance to swelling under irradiation than the presently used steels, e.g. those of type 316. These austenitic stainless steel compositions are also usable in fusion reactors.
At present the specific burn-up of fuel elements of nuclear reactors is mainly limited by the swelling of the cans containing the nuclear fuel and the hexagonal tubes containing the fuel rods. This phenomenon can lead to significant dimensional variations as a result of the agglomeration in cavities of part of the vacancies produced in the material by irradiation.
Thus, the irradiation of a material by high energy electrons, ions or fast neutrons produces in equal quantity vacancies and interstices and their creation is accompanied by a volume increase. If the temperature is sufficiently high, these defects which are produced out of equilibrium have a sufficient mobility to be eliminated by mutual recombination or absorption, or to agglomerate in the form of clusters. In the latter case, these vacancies can agglomerate and give rise to the formation of cavities and then to the growth of said cavities, which leads to a volume expansion of the material called swelling.
Hitherto, attempts have been made to limit this swelling phenomenon of canning materials by adding to the conventional austenitic alloy compositions elements such as silicon or phosphorus, as described in French Pat. No. 2 394 618, filed on 6.13.1977 by the Commissariat a L'Energie Atomique.
To further increase performances, other research has dealt with the possibility of other elements making it possible to control said swelling phenomenon under irradiation.